Real Capacity Lower than expected

[LobbyBoy]

I got a new LiFePO4 battery (12V 100 amp-hour capacity) about 4 weeks ago and have been using it in my RV as a standalone (not integrated with the RV system) power source for a 12V inverter. The discharge rate during use is typically 60-100 watts (call it 5-10 amps— usually Starlink and a reasonably efficient laptop).

I’m charging it with a 200W solar panel through a grape solar MPPT charge controller.

I’ve fitted it with a Victron Smart Shunt, which I have set up to take 14.2 volts as full, and resets itself to 100% when charged to this voltage (every sunny day so far).

Yesterday was the first day I discharged it by more than about 30 amp hours from full. The system worked well discharging at 90W until it reached 65 amp-hours of discharge (i.e. nominally still having a charge of 35 a.h.). Temperature was about 65F.

I was expecting to be able to continuing to operate until discharging more like 80 amp-hours.

Is this common? Is this one of those things that separate the better batteries from the less-so?

 

[wpns]

What brand, does it have balancing, and can you communicate with it? I take it the "90W" was a reading from the Victron Smart Shunt?

It might just need to hold at the 'fully charged' voltage for a while to balance the cells....

 

[LobbyBoy]

Eco-worthy. I can communicate with the shunt and controller. Hmm didn’t think to see if I can communicate with the battery. Will look.

 

[LobbyBoy]

Yes, using the Victron Smart Shunt to monitor discharge

 

[ChrisG]

Are the cells balanced? What does the BMS say?

 

[LobbyBoy]

As near as I can tell, I can’t interact with the BMS for this battery (Eco-Worthy 100a.hr). Have I been missing it?

 

[LobbyBoy]

Based on wpns’s post, I’m looking at my controller settings. It looks like there is an equalizing stage, which by default is off for factory LiFePO4 battery setup.

If I were to try to add an equalization stage, it calls for voltage, equalization time, and days between equalization stages. If I were to try these, what would be reasonable settings to try?

 

[Mattb4]

Do not use equalization for a LFP battery that is for lead acid. You say your battery worked until 65ah of discharge. What was the voltage of the battery at this point? Did you have any loads with high surge currents?

 

[LobbyBoy]

No, just Starlink. The voltage decreased rapidly at this point (below 11V) and the inverter started beeping. I shut it down then, disconnected the inverter, and gave it the best charge I could yesterday.

 

[Mattb4]

No, just Starlink. The voltage decreased rapidly at this point (below 11V) and the inverter started beeping. I shut it down then, disconnected the inverter, and gave it the best charge I could yesterday.

Sorta sounds like your battery has less capacity than rated. If after a good full charge (getting to 14.2 and holding for 2 hours without BMS disconnects) you experience the same discharge capacity you may have to see if there is any battery Warranty.

 

[LobbyBoy]

That’s kinda what I thought, but wanted to check here first.

Several days over the last month the battery has stayed on the charger while full, with good sunlight for yes a good hour or more.

For my understanding, if the Victron Smart Shunt is set up correctly, can I take that as a reliable way of tracking the battery inputs/outputs?

Also, how often does this happen, and how do I improve my odds when battery shopping?

 

[wpns]

how do I improve my odds when battery shopping?

To start with, I'd never buy another battery without a BMS that I could talk to with cables or BlueTooth or something. At least that way when unexpected things happen after a year or so you can gain some visibility into what's going on and why.
Lots of reviews of batteries here, and of course check out Will's video reviews and teardowns, though they tend to go out of date quickly.

 

[mikefitz]

and how do I improve my odds

Your battery is possibly OK and just needs more time at a high, greater than 13.8 volts, charge to improve balance. The default Li settings on your charger don't help, charge to 14.4 then stop charging.
You have no communication with the BMS with your battery, any future battery purchace idealy should have Bluetooth communication.
On the charger, ,perhaps select other battery types , or set user settings, that will hold the battery at high charge volts for some hours.
Note if there are unbalanced cells, and its almost certain there will be, the charge is possibility never reaching 14.4 volts. BMS shutdown of the charge path will cause the charger volts to rise to 14.4, triggering a 100 % reset on the shunt.